1. Field of the Invention
The present invention relates to a rotor for a vehicular alternating current generator which is mounted on passenger cars, trucks and the like.
2. Related Art
In a conventional vehicular alternating current generator (alternator) disclosed in JP-B2-5-34896, a field coil is wound around an insulating bobbin. The insulating bobbin has a coil-winding body part around which the field coil is wound and flanged parts extending in a radially outward direction from both ends of the coil-winding body part. A radial protrusion part and an axial protrusion part are provided on the flanged part so that a lead wire at a coil-winding start side and a lead wire at a coil-winding end side of the field coil are wound thereon respectively to restrict slackening of the field coil.
Further, in JP-A-8-331786, it is disclosed to provide a cut-out part on a protrusion part provided radially outside a flanged part, so that a field coil is press-inserted to improve rotor production work efficiency.
According to the above conventional constructions, the lead wires at the coil-winding start side and coil-winding end side of the field coil which are to be fixed to the insulating bobbin are located further outside of the radially outermost periphery of the field coil. Therefore, those parts are likely to be subjected to a centrifugal force generated during rotation of the rotor.
Particularly, in the former conventional construction, the lead wires of the field coil at the coil-winding start side and the coil-winding end side are wound around the radial protrusion part provided on the flanged part of the insulating bobbin. Thus, as a large centrifugal force is applied to the root part of the radial protrusion part during rotation, the root part is likely to fracture causing breakage of the field coil.
In the latter conventional construction, as the lead wire is inserted from the outside into the groove opening outwardly in the radial direction, the holding force against the centrifugal direction is small. If the tightening is set to withstand the centrifugal force, the intended improvement in the rotor production efficiency can not be attained.
Further, in both of the above conventional constructions, the protrusion part extending outwardly in the radial direction from the flanged part is designed to hold the field coil. This results in difficulty of sizing the rotor compact. Thus, an air flow passage in the axial direction for air-cooling the field coil is closed, and the flow resistance is increased. Further, cooling the field coil by the air flow is lessened, the output performance is lowered, and the insulating film on the field coil is deteriorated by the temperature rise in the field coil.